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Data Summary

Nitrous oxide emissions in a landscape transitioning from Conservation Reserve Program grassland to energy crops switchgrass and Miscanthus

Date

2017

Abstract

Future liquid fuel demand from renewable sources may, in part, be met by converting the seasonally wet portions
of the landscape currently managed for soil and water conservation to perennial energy crops. However, this shift
may increase nitrous oxide (N2O) emissions, thus limiting the carbon (C) benefits of energy crops. Particularly
high emissions may occur during the transition period when the soil is disturbed, plants are establishing, and
nitrate and water accumulation may favor emissions. We measured N2O emissions and associated environmental
drivers during the transition of perennial grassland in a Conservation Reserve Program (CRP) to switchgrass
(Panicum virgatum L.) and Miscanthus x giganteus in the bottom 3-ha of a watershed in the Ridge and Valley ecoregion
of the northeastern United States. Replicated treatments of CRP (unconverted), unfertilized switchgrass
(switchgrass), nitrogen (N) fertilized switchgrass (switchgrass-N), and Miscanthus were randomized in four
blocks. Each plot was divided into shoulder, backslope, and footslope positions based on the slope and moisture
gradient. Soil N2O flux, soil moisture, and soil mineral nitrogen availability were monitored during the growing
season of 2013, the year after the land conversion. Growing season N2O flux showed a significant vegetation-bylandscape
position interaction (P < 0.009). Switchgrass-N and Miscanthus treatments had 3 and 6-times higher
cumulative flux respectively than the CRP in the footslope, but at other landscape positions fluxes were similar
among land uses. A peak N2O emission event, contributing 26% of the cumulative flux, occurred after a 10.8-cm
of rain during early June. Prolonged subsoil saturation coinciding with high mineral N concentration fueled N2O
emission hot spots in the footslopes under energy crops. Our results suggest that mitigating N2O emissions du